The present invention relates to stirrers and more particularly to stirrers for stirring molten glass.
It is known to stir molten glass in a glass melting tank by use of stirrers which pass down through openings in the roof of the glass tank or furnace, down through the atmosphere above the molten glass and into the molten glass. The supporting and driving means for the stirrers is located outside the furnace and is thus protected from the high temperature and atmosphere within the furnace. Difficulties arise in manufacturing the parts of the stirrers which are located within the molten glass or atmosphere within the furnace as they must withstand the corrosive nature of the molten glass and of the atmosphere. Molybdenum has been used in the manufacture of stirrers but molybdenum is readily attacked by oxygen and difficulties have arisen with parts of the stirrer exposed to the atmosphere within the glass furnace. In view of this proposals have previously been made to clad stirrers totally with a platinum coating. Platinum is not seriously affected by the oxygen although some volatisation occurs. However, platinum is liable to attack due to the fact that the presence of any aluminium in the molten glass results in silicon attack. Aluminium can be present as a contaminant in batch materials.